This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Staphylococcus aureus causes a wide variety of diseases in both humans and animals. Although largely unreported, staphylococcal infection of the mammary gland, or mastitis, affects millions of women each year - nearly 33% of nursing mothers. Unfortunately, studies have determined that mastitis in women is a significant cause for the cessation of breast-feeding. This is particularly significant given that the benefits of breast-feeding have now been well documented. For example, these benefits include protection of the infant against diarrheal and respiratory diseases, ultimately leading to a lower risk of postneonatal death. In addition, breast-fed infants exhibit a reduced risk of obesity and cardiovascular disease in adulthood. Perhaps more alarming are studies showing that mastitis in HIV-infected women is a major risk factor in the transmission of this virus from mother to infant. Despite the impact of mastitis on human health, little is known about the host-pathogen interactions that occur with mastitis. Recent studies have demonstrated that the lipids found in milk have profound effects on pathogens such as S. aureus. For example, glycerol monolaurate (GML) has an inhibitory effect on the growth of S. aureus and inhibits the expression of virulence factors in S. aureus at subinhibitory concentrations. The active agent in GML as indicated by our preliminary studies appears to be the free fatty acid, lauric acid. In addition, our studies indicate that other fatty acids commonly found in milk possess antimicrobial activity. Thus, lipids may not just be an energy source for the nursing infant;many fatty acids made available by the action of both bacterial and mammalian lipases may also play a role in minimizing the impact of pathogens on the host through inhibition of bacterial growth and virulence. Therefore, the overall objective of this proposal is to test the hypothesis that specific fatty acids and lipases impact the progression of staphylococcal mastitis. This hypothesis will be tested in three specific aims including: 1) To determine the fatty acids and form of lipid that regulate the growth and expression of virulence factors in S. aureus. In this aim we will determine the range of fatty acids present in milk that affect growth and virulence factor production in S. aureus. 2) To examine the regulation and significance of lipase activity in S. aureus and the mammary gland as a mechanism to provide benefits to the pathogen and/or host. Here, we will study the role of both pathogen- and host-encoded lipases on milk lipid metabolism and determine their potential roles in the progression of disease within mammary tissue. 3) To compare the effects of altered milk lipid composition on the host-pathogen response to an infection with S. aureus. This aim will address the impact of altering the lipid composition of milk, through dietary supplementation, on the resistance and severity of staphylococcal mastitis. The results of these studies will have a major impact on our understanding of the host-pathogen interactions that occur within the mammary gland and could lead to novel strategies to reduce these types of infections in women.